1. Field of the Invention
The present invention generally relates to intra-train communications for implementing Electrically Controlled Pneumatic (ECP) railroad freight train brakes and, more particularly, to a multi-function End of Train device (EOT) that operates in a standard mode in which the EOT functions as a normal EOT, in an ECP mode providing ECP functionality in an ECP type of EOT device, or in an emulation mode in which the EOT has 74 V train line power but otherwise functions as a normal EOT.
2. Background Description
End of Train (EOT) signaling and monitoring equipment is now widely used, in place of cabooses, to meet operating and safety requirements of railroads. The information monitored by the EOT typically includes the air pressure of the brake line, battery condition and train movement. A warning light is incorporated into the EOT housing, and the operation of this warning light is also monitored. This information is transmitted to the crew in the locomotive by a battery powered telemetry transmitter.
The original EOT telemetry systems were one-way systems; that is, data was periodically transmitted from the EOT to a Locomotive Control Unit (LCU), sometimes referred to as the Head of Train (HOT) unit, mounted in the locomotive where the information was displayed. Later systems are two-way systems in which transmissions are also made by the LCU to the EOT. In one specific application, the EOT controls an air valve in the train's brake pipe which can be controlled by a transmission from the LCU. In a one-way system, service and emergency brake application starts at the locomotive and progresses along the brake pipe to the end of the train. This process can take significant time in a long train, and if there is a restriction in the brake pipe, the brakes beyond the restriction may not be actuated. With a two-way system emergency braking can be initiated at the end of the train independently of the initiation of emergency braking at the head of the train, and the process or brake application can be considerably shortened. As will be appreciated by those skilled in the art, in order for an LCU to communicate emergency commands to an associated EOT, it is desirable for the EOT to be "armed"; that is, authorized by railroad personnel. This is desirable to prevent one LCU from erroneously or maliciously actuating the emergency brakes in another train. To this end, the LCU includes a nonvolatile memory in which a unique code identifying an EOT unit can be stored. The LCU also has a row of thumb wheel switches which allows manual entry of codes. Additional background on EOT systems may be had by reference to U.S. Pat. Nos. 5,374,015 and 5,377,938, both to Bezos et al. and assigned to the assignee of this application.
The Federal Communication Commission (FCC) allocates blocks of radio frequencies for railroad communications. The Association of American Railroads (AAR) then further allocates the frequencies on a channel basis, which are then used by radio-based intra-train communications systems. The AAR develops standards for the railroad industry for, among other things, intra-train communications. Most recently, the AAR is considering an intra-train communication system in which all the cars in a consist are hard wired together. In such a system, power to and communications with the EOT is provided over a cable extending the length of the train. To this end, the AAR has promulgated draft specifications for Electrically Controlled Pneumatic (ECP) Freight Brake Systems, revision #9, Nov. 27, 1996, that requires a special EOT device, hereinafter referred to as an ECP EOT, as specified on page 2, paragraph 2.1.6. As specified in that paragraph, this special ECP EOT will contain a "neuron" chip (a commercially available integrated circuit (IC) chip), a brake pipe pressure transducer and a battery which will be charged off the train line voltage. Presumably, this ECP EOT will also need a standard marker warning light, although the specifications fail to mention this.
Since freight trains can be a mile or more in length, the AAR has determined that the voltage on the cable must be 230 VDC in order to provide adequate power to the ECP EOT. To insure safety of personnel and continuity of the cable, it is necessary to transmit status signals from the ECP EOT to a Head End Unit (HEU) (as distinguished from an LCU in non-ECP EOT systems). First, before the 230 VDC power can be turned on, it is necessary to insure the safety of personnel to make sure that the cable has been properly terminated in the ECP EOT and does not pose a shock hazard. When the cable has been properly terminated, the ECP EOT, under battery power, listens for a beacon from the HEU and, upon detecting a beacon, communicates this to the HEU via the 230 VDC power lines, confirming continuity of the 230 VDC power lines and allowing the engineer to turn the 230 VDC power on or allowing the HEU to automatically turn the 230 VDC power on. In addition, since the 230 VDC line could be broken either intentionally or accidently, the ECP EOT must periodically transmit a status message to insure the continued continuity (i.e., no breaks) of the 230 VDC cable connection, thus further insuring personnel safety.
The AAR specifications suggest that the ECP EOT should be a different unit from the currently manufactured standard two-way EOT, owing in part to the specification for the "neuron" microprocessor and power line modem transceiver and the fact that the cable interface eliminates the need for a high capacity rechargeable battery to power the EOT. However, railroads which use this equipment want to standardize equipment to minimize the logistics of their inventory and maintenance. Manufacturers of the equipment also want to standardize their products in order to improve quality and realize savings.